The United Nations said Thursday's US Supreme Court ruling that curbs regulators' power to limit greenhouse gas emissions had dealt a blow to the fight against global warming.
"This is a setback in our fight against climate change," said Stephane Dujarric, spokesman for Secretary-General Antonio Guterres.
By a majority of 6-3, the US high court said the Environmental Protection Agency did not have the power to set broad caps on emissions from coal-fired power plants.
The decision sets back President Joe Biden's hopes of using the EPA to bring down emissions to meet global climate goals, set in 2015 under the Paris Agreement on climate change.
Mr Dujarric said the world is far off course to meet the goals of that accord. "Decisions like the one today in the US or any other major emitting economy make it harder to meet the goals of the Paris Agreement, for a healthy, liveable planet, especially as we need to accelerate the phase out of coal and the transition to renewable energies," he said.
He added however that "the actions of a single nation should not and cannot make or break whether we reach our climate objectives."
Mr Biden's administration is currently working on new regulations. The court's six conservatives were in the majority in the decision authored by Chief Justice John Roberts, with the three liberals dissenting.
Mr Biden called the ruling "another devastating decision that aims to take our country backwards."
"While this decision risks damaging our nation's ability to keep our air clean and combat climate change, I will not relent in using my lawful authorities to protect public health and tackle the climate crisis," he said in a statement.
The Democratic president said he directed his legal team to work with the Justice Department and affected agencies to review the ruling and find ways under federal law to protect against pollution including emissions that cause climate change.
The ruling is likely to have implications beyond the EPA as it raises new legal questions about any big decisions made by federal agencies.
The court's conservative majority has signalled scepticism toward expansive federal regulatory authority. Conservative legal activists have long advocated reducing agency power in what has been called a "war on the administrative state."
The justices overturned a 2021 decision by the US Court of Appeals for the District of Columbia Circuit that had struck down Republican former President Donald Trump's Affordable Clean Energy rule.
That regulation, which Mr Biden's administration does not plan to retain, would impose limits on a Clean Air Act provision called Section 111 that provides the EPA authority to regulate emissions from existing power plants.
Mr Trump's rule was meant to supplant Democratic former President Barack Obama's Clean Power Plan mandating major reductions in carbon emissions from the power industry.
Thursday's ruling was based on what is called the "major questions" legal doctrine that requires explicit congressional authorisation for action on issues of broad importance and societal impact.
The justices in January appeared to embrace that theory when it blocked the Biden administration's vaccine-or-test policy for larger businesses, a key element of its plan to combat the COVID-19 pandemic.
The court's invocation of this doctrine sends a signal that the justices will be a major obstacle to federal agencies seeking to implement broad policies of national importance.
The decision will constrain the EPA's ability to issue any regulations on power plants that push for an ambitious national shift in energy policy toward renewable sources.
As such, it will hamstring the administration's ability to curb the power sector's emissions, about a quarter of US greenhouse gases.
Mr Biden's administration wants the US power sector decarbonised by 2035. The United States, behind only China in greenhouse gas emissions, is a pivotal player in efforts to combat climate change on a global basis.
Thursday's decision came on the final day of rulings for the court's current nine-month term.
